Long Term Evolution (LTE) is a Third Generation Partnership Project (3GPP) standard for mobile network technology. The LTE describes a plurality of requirements for mobile communications systems in evolved or advanced cellular broadband technologies. Such requirements include Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), which is a high-speed radio access technique to meet the increased network demands, including improving user throughputs and network capacity, reducing latency, and increasing mobility. For instance, the LTE uses an Enhanced Packet Core (EPC) network architecture to support the E-UTRAN. The EPC network architecture uses protocols such as Transmission Control Protocol (TCP)/Internet Protocol (IP) for supporting IP based services, such as voice, video, other media, and messaging, with end-to-end Quality of Service (QoS). The EPC network architecture also enables improved connections and hand-over to other fixed-line and wireless access technologies with improved mobility.
The LTE Physical Layer (PHY) uses advanced technologies, including Orthogonal Frequency Division Multiple Access (OFDMA), multiple-input and multiple-output (MIMO) data transmissions, and smart antennas to meet the network demands above. The LTE PHY uses OFDMA for downlink transmissions, for instance from a Base Station (BS) to a User Equipment (UE), which can communicate by transmitting signals throughout a geographical region known as a cell. Additionally, The LTE PHY uses Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink transmissions, for instance from the UE to the BS. The OFDMA and SC-FDMA technologies reduce the LTE and UE system complexities and increase the communication spectrum or bandwidth.
The UE may be any mobile device used in the LTE system, such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. The UE may consist of a wireless device and its associated Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application or might consist of the device itself without such a card. Alternatively, the UE may be a device that has similar wireless capabilities but that is not transportable, such as desktop computers, set-top boxes, or network nodes. The UE may also be a network node, which acts on behalf of another function, such as a wireless device, and simulates or emulates the device. For example, for some wireless devices, an IP Multimedia Subsystem (IMS) Session Initiation Protocol (SIP) client that would typically reside on the device actually resides in the network and relays SIP message information to the device using optimized protocols. In other words, some functions that were traditionally carried out by a wireless device can be distributed in the form of a remote UE, where the remote UE represents the wireless device in the network. In some instances, the UE may be any hardware or software component that can terminate an SIP session.
In addition to the BS and UE, LTE systems may include advanced equipment, which provide services that were not possible previously, such as an enhanced node B (ENB). These devices can provide at least some of the functionalities of the BS, wireless access points, and other systems and devices some of which may be more evolved than the equivalent equipment in a traditional wireless telecommunications system. The term ENB or access device may be used herein to refer to any device, existing or advanced, that may be used to gain access to a network. Such advanced or next generation equipment may be referred to herein as long-term evolution (LTE) equipment.
The LTE includes protocols such as a Radio Resource Control (RRC) protocol, which is responsible for the assignment, configuration and release of radio resources between the UE and the BS, ENB or other access or LTE equipment. The RRC protocol is described in detail in the 3GPP TS 36.331 specifications. According to the RRC protocol, the two basic RRC modes for the UE are defined as “idle mode” and “connected mode.” During the connected mode or state, the UE may exchange signals with the network and perform other related operations, while during the idle mode or state, the UE may shut down at least some of its connected mode operations. Idle and connected mode behaviors are described in details in the Third Generation Partnership Project (3GPP) specifications TS 36.304 and TS 36.331.